Rotary tools, including drills, grinders, and routers, include a tool retainer or holder that non-rotatably secures a rotary bit (e.g., a cutting tool such as a drill bit or a router bit) to a drive shaft that is rotated by the rotary tool. One bit that has been developed for use in such rotary tools is a sanding drum bit. A sanding drum bit includes one end portion adapted for engagement with the bit holder and a second end portion which is adapted to support a closed loop sanding belt.
In order to mount the closed loop sanding belt on the sanding drum bit, the closed loop sanding belt must be somewhat larger in diameter than the mounting portion of the sanding drum bit. Configuring the closed loop sanding belt to fit onto the sanding drum bit in such a fashion, however, introduces the potential for the closed loop sanding belt to slip (radial relative movement) or creep (axial relative movement) on the sanding drum bit in use. Various approaches have been used to overcome this problem.
One approach used to minimize slip and creep is to minimize the difference in diameter between the closed loop sanding belt and the sanding drum bit mounting portion. Of course, as the mismatch is reduced, the difficulty in mounting the closed loop sanding belt on the sanding drum bit increases. In another approach, the frictional force between the sanding drum mounting portion and the sanding belt is increased by selecting high friction materials. For example, in some sanding drum bits, the mounting portion of the bit is made from a rubber material. This increases the amount of friction that must be overcome before creep or slip is realized. At the same time, the increased friction makes mounting of the closed loop sanding belt on the sanding drum bit mounting portion more difficult.
In some sanding drum bits, the mounting portion is configured to provide a variable diameter. In these devices, a rubber cylinder is compressed lengthwise, such as by using a screw and washer arrangement. As the length of the rubber cylinder is reduced, the diameter of the rubber cylinder is increased. Accordingly, a closed loop sanding belt can be mounted on the sanding drum bit with the rubber cylinder uncompressed. Once the closed loop sanding belt is mounted, the rubber cylinder is compressed to increase the friction between the closed loop sanding belt and the sanding drum bit. While effective, this approach can cause delay in changing between closed loop sanding belts. For example, a user must find a screwdriver to manipulate the screw and washer arrangement. Then, the screw and washer arrangement must be loosened to allow removal of a first closed loop sanding belt, and then tightened after a new closed loop sanding belt is positioned.
In another approach, some sanding drums have been constructed with recessed inset areas into which a sanding belt is snugly fitted. This approach is a costly modification since the sanding drum and sandpaper must be made with complementary non-planar surfaces. In addition, seating of the belt must be exact, otherwise slippage will be exacerbated.
What is needed is a sanding drum assembly that provides increased resistance to slip or creep. A further need exists for a sanding drum assembly that reduces the number of tools needed to replace sanding belts. Yet another need exists for a sanding drum assembly that allows for rapid replacement of sanding belts.